1. Field of the Invention
This invention is related to the field of lock mechanisms and, more particularly, to automatic lock mechanisms.
2. Description of the Related Art
Security is an increasingly important concern for both home and business. Despite the existence of numerous types of alarms and electronic security systems, the primary barrier to unauthorized entry in most cases is a locked door, and an important factor contributing to an overall level of security is the impregnability of the lock.
Furthermore, in situations calling for frequent entry and egress, such as a home, convenience is also an important consideration. No matter what advantages a lock may offer, if it is overly complicated or requires a great deal of effort to operate, people will tend to avoid using it. Users often deliberately circumvent elaborate, but inconvenient, security systems.
It is well known that deadbolt lock mechanisms provide greater security and are more resistant to unauthorized entry than conventional doorknob key locks. Unfortunately, standard deadbolt mechanisms lack the convenience of key locks, and therefore, are less frequently used than they might otherwise be. While the majority of doorknob key locks can be set to automatically lock the door when it is closed, a deadbolt lock typically must be locked from the outside with a key. Upon leaving a building, an additional step is therefore required to secure it with a deadbolt lock, compared with the automatic locking feature of the doorknob key lock. This may be sufficient encouragement for people to forego the greater security of the deadbolt. An automatic mechanism that engages a deadbolt without the need for a key would add greatly to the convenience of the deadbolt lock. This, in turn, would conduce to wider use of the deadbolt lock, and enhanced security.
Previous approaches to automatic locking mechanisms suffer from a variety of drawbacks. Many of these designs employ electronic timers or actuators. For example, U.S. Pat. No. 3,677,043 to Cox describes an electrically-actuated remote control door lock. Electronic timers are capable of great precision and longevity, and they can be readily integrated with other intrinsic circuitry, e.g., as in an electronic combination lock. However, in the event of power loss such mechanisms may become ineffective. In the worst case, this could mean leaving a door unsecured, or on the other hand, locking out individuals with rightful access. Other approaches to automatic locking make use of pneumatic timing devices. For example, U.S. Pat. No. 4,643,106 to Aragona describes a method for automatically relocking a lock after a prescribed time delay, in which the time delay depends on the compression of air by a piston and cylinder. There are problems with such designs, however. The seals in dashpots and similar devices are prone to wear and subject to temperature changes, which may result in substantial variation in the timing characteristics.
The problems outlined above are in large part solved by an automatic deadbolt locking mechanism as described herein. The mechanism comprises a deadbolt lock with means for automatically engaging the lock, along with a mechanical timer. The mechanical timer may comprise a system of gears and a coil spring. When the key, or a thumbturn, is turned to unlock the door, the primary gear within the system of gears may be made to rotate, winding the spring and simultaneously compelling the other gears to rotate at a rate determined by their relative gear ratios. The speed at which the primary gear rotates may be determined, for example, by a small propeller or centrifugal weights, as are commonly employed in mechanical clocks. The time required for the spring to completely unwind and restore the gears to their initial orientations constitutes the timer interval.
The deadbolt lock further comprises a deadbolt, which may be pushed into the locked position by a compression spring. Gear teeth on the deadbolt may mesh with teeth on a drive gear, such that when the key or thumbturn is turned the deadbolt is retracted from its locked position. A catch prevents the deadbolt from returning to the locked position until the timer runs down. The catch may be disengaged by a cam on one of the timer gears that, when rotated into position, lifts the retaining catch and releases the deadbolt. Once this happens, the compression spring immediately thrusts the deadbolt into the locked position.
Thus, unlocking the door may activate the deadbolt locking mechanism. Upon this unlocking of the door, after a prescribed interval the timer may automatically reengage the deadbolt lock. Additionally, in one embodiment, a pushbutton may be included in the mechanism that enables or disables the timing mechanism. This function may be useful if it is desired to allow the door to remain unlocked for some period of time.
A method is also contemplated herein for automatically relocking a deadbolt, after a prescribed time interval subsequent to unlocking the door. This method may further comprise means for optionally disabling automatic operation, allowing the mechanism to function as a conventional deadbolt lock.
The method and mechanism described herein are believed to be advantageous by providing increased convenience when using a deadbolt lock. Deadbolt locks are known to offer greater security against unauthorized entry than doorknob locks. Automatic activation of a deadbolt is believed to increase the likelihood that the deadbolt lock will be used. A mechanical design as described herein is believed to have inherently greater reliability than other designs, such as power-dependent electronic systems, pneumatic or hydraulic systems.